The present invention relates to use as a rope position sensor for sensing the position of a rope in a groove in a pulley and to a pulley assembly equipped with at least one such sensor.
There are many types of transport installations using wire ropes to ensure the traction of a vehicle, e.g. ski-lifts or chair lifts, funiculars, or cableways of any kind. Such ropes are running on pulleys serving for their guidance. Cableways generally comprise one or several carrying ropes. In this case, pulleys fastened to the vehicle serve as wheels on which the vehicle runs along the carrying rope.
Pulleys for wire ropes are provided with a circular groove which receives the rope and thereby defines the normal position of the rope with respect to the pulley in the radial and lateral directions. For the safety of the transport installations it is important that the rope always keeps this normal position on the pulleys. If a rope is misaligned with respect to the groove and runs to the left or to the right of the groove, this indicates a malfunction of the installation that may lead to the derailment of the rope in the worst case, i.e. to a situation where the rope is no longer on the pulley at all. For safety reasons, it is very important to detect such irregular situations. They generally require an immediate stop of the installation. Another anomaly that must be detected is a locked pulley, in which case the rope will wear away the pulley and gradually approach the rotation axis of the pulley.
A sensor for monitoring the position of the rope relative to the pulley is described in International Patent Application WO-99/27649. This sensor comprises several zones of influence in which it is capable of detecting the presence of the rope by means of proximity detectors. A sensor having three zones of influence has three signal outputs, and the signal at each one of the outputs indicates for a particular zone of influence, whether the rope is being detected in that zone or not. It is possible that a rope is being detected in two zones of influence simultaneously. This sensor comprises a distinct proximity detector for the surveillance of each zone. It is expensive, and its lifetime is limited as the risk of electronic malfunction of a proximity detector is multiplied by the number of detectors used in the sensor. Moreover, the verification of the correct operation of such a sensor is laborious since a plurality of proximity detectors have to be tested.